The most basic description of an audio mixer is it routes various signals into a common output for amplification or recording through the help of a sound reinforcement system. These signals include the sounds captured by an electric instrument or a microphone.
Audio Mixer Console Functions
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An audio mixer is a very powerful tool that will allow you to record and mix whatever audio you want for your media. But since it can be very expensive and impractical to get one yourself, you need to hire a professional to be in charge of this aspect of your work.
What is an Audio Mixer?
Audio mixers are also called desk, board, or console. This device can range from a large-format giant mixer usually found in professional studios to tabletop audio mixers used by amateurs and newbies in the industry. The varieties of this device cater to live sound, film and television audio, music production, broadcast, and voice-over outputs.
Mixers share the same function and features that are vital in mixing audio. Some of the requisite features of mixers include EQ, pan pots, faders, preamp, and XLR inputs with adjustable trim and aux busses. For large-format audio mixers, they may have additional features.
Types of Audio Mixers
Audio mixers can be analog, digital, or a mixture of both. Digital audio mixers are most popular.
The original mixers were based on analog technology, and they were used for live and studio recording. Some engineers prefer the warmer sound of a genuine analog mixer. Depending on the amount of effects, analog mixers can be large in size.
Digital mixers are more compact, but offer a variety of essential effects. Modern technology has led to minimizing the amount of faders, without reducing any inputs. Motorized faders let you flip from one bank to another, and the faders will automatically shift into position.
Many digital mixers come with a recording function. This is very useful for rehearsing new material, as well as recording. Recording practice sessions, can sometimes produce great recordings, which can be used as demos. You can create album-quality recordings with just your mixer.
Most mixers will record the master mix to an internal memory, an SD card, or USB. Sometimes the file is immediately compressed. To make the best quality, multi-track recordings, you will need a mixer that doubles as an audio interface. This will allow you to connect it directly to a computer and record the final mix to a DAW.
Channels
The channels will be lined up on the left of the control panel. Each channel has an input and a number of controls for that channel. Mixers come in all sizes. Some only have 2 channels, and others can have over 50 channels.
Mixers come with a variety of different controls, but basic controls are very similar. The channel input combined with its set of dedicated controls is always referred to as a channel strip. Channel strips can also be a separate device.
The amount of channels nedded, depends on the size of the band, that you want to mix. It’s always better to have too many channels than not enough. A band with a standard setup can quickly use up to 16 channels. If you are working with multiple bands, you may want the option to save some settings. This is done with presets. Bands may have their own microphones or additional instruments. It is important to have the right amount of physical channels.
Some mixers only offer a limited number of preamps compared to the total number of inputs. This results in having leftover line-inputs that don’t have preamps. A minimum of twenty-four channels is recommended.
Each channel will be equipped with a fader, to control the channel volume. Smaller mixers may have rotary knobs instead of faders. When you set the channel faders, you set the signal level of the channels as they are sent to the output. Most channel strips have two or three controls for equalizing.
Equalizer
On most mixers, the EQ knobs are lined up underneath the channel gain knob. Equalizer controls are only used to cut or boost specific frequencies.
The equalizier adjusts the high, middle, and low frequencies of the audio signal. It allows you to add more bass or remove the treble. The mute button silences the channel. Some mixers will send the signal to a different output, to be used as a sub-group.
Mixers also offer an EQ section for the master signal. These are usually small faders that are used to adjust the total sound. It can help boost or neutralize any bad frequencies or acoustics, during a performance.
Inputs
Mixers can come with a variety of different inputs. The mono channels usually have two inputs. The XLR is a microphone input, and a line input for a 6.3mm jack. Mono channels will have just a line-input or microphone input. Most mixers come with stereo line-inputs, and a pair of jack ports, for left and right stereo channels.
Using A Preamp
The first part of the signal path, is where the instrument connects to the mixer. It will be either a microphone or line input. A microphone input has a lower output volume than a line level signal. Microphone inputs usually have a gain-boosting preamp, to strengthen the signal. The level of boost is controlled using the gain/trim knob that’s usually found at the top of the channel strip.
Preamps can raise the volume of the input signal, and can make a significant difference to the quality of sound. This is determined by the character of the preamp, and how it colors the signal. The sound difference is more noticeable in the studio than in a live setting.
In order to benefit from the depth and dimensions of a preamp, you will find better quality in more expensive models. Many sound engineers use more than one external preamp, to acheive specific sounds from vocals, guitars, or drums.
Phantom Power
Phantom power is the primary standard for powering professional condenser microphones. Condenser microphones need 48 Volts of power in order to function. This is called phantom power and it is fed to the microphone from the mixer, through the XLR port. There is a power function switch to activate the phantom power.
-10DBV & +4DBU
The two standards for the level of a line signal are -10 dBv and +4 dBu.
Professional studio equipment almost always operates using the higher level of +4dBu.
Hi-fi equipment and instruments like keyboards use a lower level of -10dBv.
Most mixers have a -10 dBv and +4 dBu selector switch. It connects to both to the inputs and the outputs. If you connect a portable recorder, with -10dB, to an output that’s is +4dBu, the signal will sound distorted. The selector switch allows you to switch the output to the right setting, and correct the distorted sound.
Balance
The microphone inputs are usually balanced to counter any microphone signal interference. Having a good quality mixer, will ensure that every input, output, and line signal is balanced.
You should use a stereo jack cable with a balanced jack port. A mono jack will work without any issues, but you wont get the full features of having balanced inputs and outputs. They are usually labeled BAL or UNBAL.
Microphones
The aux send and aux return features are used to add parallel effects to the sound. The aux send taps off the signal. It runs through an effects unit and then is added back to the original signal through the aux return. An effect like reverb is a typical parallel effect. It is always looped through the aux send and return. Each channel has a control knob for setting how much of the signal is fed through the aux send. It can be set to zero if a specific channel doesn’t need to be treated with the parallel effect.
Active DI boxes and condenser microphones have no voltage at all. These are fed phantom power through the mixer via the connected XLR cable. If you are using a ribbon microphone or equipment that is sensitive to electric current, you want a mixer with a phantom power switch per channel. Only use the phantom power on/off switch when the channel is muted, or the gain is all the way down. If not, there will be an electronic pop. At high volumes, this can be damaging to the ears.
Auxilliary Send & Return
When a line output, from an instrument, is connected to a microphone preamp, a lot of gain is generated. The result will be a lot of distorted noise. Line signals are usually unbalanced. When bridging longer cables over longer distances, your signal will become more sensitive. It will pick up noise and interferences caused by electro-magnetic radiation. A DI box can be used to weaken, and balance the high voltage of the line signal. It can then be sent out as a microphone level to a mixer.
Some mixers have a control knob for adjusting the overall volume of all the aux sends. There will also be a knob for controlling the level of the processed signal coming back through. The aux send can be used to connect a monitor. Every aux knob on every channel will be used to determine the level of each channel as it’s sent to the connected monitor.
The aux return can be set up as an extra stereo or mono line input. If you use it as a line input, you can only control the volume. You wont be able to adjust the EQ.
The auxiliary send feature is fixed under the EQ section. The auxiliary send lets you independently send each track to a separate output. The output can lead to an effects unit or a monitor. The auxiliary return can be a rotary knob or a separate fader. It determines how much of the processed signal is mixed with the original signal. This allows all of the channels of the mix to be run through the same effect.
This feature helps you create clean and solid mixes. It can also save space and money. When choosing the right mixer, make sure to consider all the equipment in your setup. It is important to have enough auxiliary functions to work with.
Pre & Post Fader
An aux send can be tapped before or after the fader, the channel volume control. The settings are pre, before, and post, after. There is usually a button for pre or post fader next to the aux send knob.
Post fader maintains the same proportion as the original signal. and can be adjusted by the fader setting. Pre fader means the aux send signal remains constant, regardless of the fader setting. This is great when you need to use the aux send as a monitor signal.
Stereo Monitors & Control Room Output
In addition to the stereo main output, mixers will also have a stereo monitor or control room (C/R) output. This output can be connected to an amplifier or active monitors, so you can listen to the total mix. The C/R output has its own volume control. The main output volume is not affected by the C/R volume. You can connect your instrument to mixer and to the main output of a PA. At the same time, you can connect the C/R output to your own monitor. You can control your monitor volume with the C/R volume control, without affecting the volume level sent to the PA.
For smaller mixers, the exact same mix is sent through both the main output and the C/R output. For larger mixers, every channel will have a solo button to send the signal through C/R output. This allows you to use the C/R output to isolate and listen to one or more channels without messing with the main output mix.
All mixers have a headphone output which is coupled with the C/R output. The mix you hear through your headphone will be the same mix being sent through the C/R output. The headphone volume is controlled by the C/R volume.
Main Out
The main output sends the mixed stereo sound from your mixer to your amplifier and speakers. This controls the volume of the sound that the audience will hear. On smaller mixers, the volume of the main mix is set with a rotary knob. Larger mixers have a set of two faders, for the left and right of the stereo equipment.
There should be a row of colored LED lights, which is the level meter. The lights indicate how loud the main output signal is. A high level is always red. If the LED lights are red, it means the signal is too loud and will be distorted. Larger mixers have a dedicated equalizer for the main out. This allows you to add more detail and balance to the final mix.
